Studies on the Hydrolytic Behavior of Zirconium

• The stability constants of zirconium(IV) hydrolysis species have been measured at15, 25, and 35°C [in 1.0 mol-dm-3 (H,Na)ClO4] using both potentiometry and solventextraction. In addition, the solubility of [Zr(OH)4(am)] has been investigated in a 1 moldm-3 (Na,H)(ClO4,OH) medium at 25°C over a wide range of -log [H+] (0-15). The results indicate the presence of the monomeric species Zr(OH)3+, Zr(OH)2+2, Zr(OH)+3,and Zr(OH)04(aq) as well as the polymeric species Zr4(OH)8+8 and Zr2(OH)2+6. The solventextraction measurements required the use of acetylacetone. As such, the stability constants of zirconium(IV) with acetylacetone were also measured using solvent extraction.All stability constants were found to be linear functions of the reciprocal oftemperature (in kelvin) indicating that ΔHo and ΔSo are both independent of temperature(over the temperature range examined in the study). The results of the solubilityexperiments have shown four distinctly different solubility regions. In strongly acidicsolutions, the solubility is controlled by the formation of polynuclear hydrolysis speciesin solution whereas in less acidic solution the formation of mononuclear hydrolysisspecies becomes dominant. The largest portion of the solubility curve is controlledby equilibrium with aqueous Zr(OH)04(aq) where the solubility is independent of theproton concentration. In alkaline solutions, the solubility increases due to formationof the zirconate ion. The middle region was used to determine the solubility constant(log ∗Ks10) of Zr(OH)4(s). From the data in the alkaline region, a value of the stabilityof the zirconate ion has been determined. This is the first time that the possible evidencefor the zirconate ion has been identified in aqueous solution that has previously beenfound only in the solid phase.

Subject headings

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Keyword

hydrolysis

thermodynamics

temperature

solvent extraction

Zirconium

potentiometry

solubility

Publication and Content Type

art (subject category)

ref (subject category)